U.S. Pat. No. 1,694,937 discloses a floor scrubbing machine, which is capable of picking up dirt and water from a floor by two cylindrical floor brushes disposed parallel and close together and rotated at high speed, one running clockwise and the other counter clockwise, the adjacent peripheries traveling together and with velocity sufficient to project the dirt and water vertically upward with considerable force in the form of a substantially flat jet. A deflecting or baffling means is provided above the brushes, whereby the upward jet, after having risen clear of the brushes, is checked and diverted to a dirt receptacle.
The action in respect of the upward delivery of dirt and water in the scrubbing machine appears to be as follows. Individual masses of dirt and liquid, discharged by centrifugal force from the periphery of a brush, either strike the periphery of the opposite brush and are impelled upward again, or they collide with similar masses thrown off from the other brush, resulting in the dirt and water shooting vertically upward clear of the brushes in the form a substantially flat jet. Practically all of the dirt and water is thrown off from the brushes during the first half revolution. The brushes arranged and operating in the manner as described lift the water without additional suction means or any elevating devices.
It is stated that the high speed brushes remove practically all the water from the floor. However, it is possible that a small amount remains. In order to collect such small amount, the scrubbing machine is equipped with a wiper or a squeegee.
EP 0 169 850 discloses an apparatus that has many aspects in common with the scrubbing machine known from U.S. Pat. No. 1,694,937. In particular, EP 0 169 850 discloses an apparatus for cleaning of preferably hard surfaces like floors, stairs and the like. The apparatus has two against each other rotating, substantially cylindrical brushes, through which the apparatus is supported on the surface, and means for supply of liquid detergent to the brushes, wherein the brushes are arranged to transport dirt particles by means of their rotation between them to at least one container.
The apparatus rests with its brushes against the surface to be cleaned in such a way that their bristles are deformed at the contact with the surface when the brushes rotate. The bristles are moistened, and when the bristles come into contact with the surface, liquid detergent is brought to the surface and binds the dirt particles which to some extent also stick to the bristles. At the contact with the surface, the bristles are bent backwards. As a result, an area contact is achieved instead of a line contact. The bending of the bristles comes to an end when the bristles, during continued rotation, lose contact with the surface, whereby dirt particles are thrown in a tangential direction because of a fast straightening of the bristles. Scraping edges are applied in order to ensure that dirt particles that may remain on the bristles will be scraped away and fall down to the surface in order to be thrown up by the bristles a next time.
It appears from the foregoing that the use of two counter-rotating brushes for cleaning a floor is known in the art. Furthermore, it appears that additional means are used as well in order to achieve acceptable cleaning results. In the scrubbing machine known from U.S. Pat. No. 1,694,937, a wiper or a squeegee is applied in addition to the brushes in order to have a dry floor. In the apparatus known from EP 0 169 850, scraping edges are applied in order to ensure proper continuous cleaning of the brushes in the apparatus, wherein dirt particles fall down to the surface to be cleaned. These dirt particles need to be picked up again, wherein there is a risk that they stick to the brushes once again, and are made to fall down to the surface to be cleaned once again. Other disadvantages reside in the fact that the use of scraping edges increases the power needed for rotating the brushes, wherein a rate at which the brushes suffer from wear and tear is increased as well, and in the fact that during contact of the brushes to a surface to be cleaned, forces such as elastic forces are exerted on the surface, which are generated by the individual bristles, as a result of which friction forces and heat are generated, which may lead to damage of the surface.
It is an object of the present invention to realize a use of at least one rotatable brush for cleaning a surface with an optimal combination of operating parameters, i.e. a combination of operating parameters which ensures an optimal cleaning function of the brush, wherein there is no need for additional means for performing a cleaning action on a surface besides the brush, or for additional means for keeping the brush clean during operation. In other words, it is an object of the present invention to find an optimal combination of operating parameters for the brush, wherein it is possible to clean and dry a surface by only using the functionality of the brush.